Fix crash on Linux on startup

[veler]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the current behavior?

In GTK 4.10 on Ubuntu, using either GTKSharp or Gir.Core NuGet package, we're unable to invoke gtk_file_dialog_new to create a new file dialog. Why? I have no clue.

What is the new behavior?

Workaround this issue by using GTK's FileChooserNative API.

Other information

This PR also includes a small refactoring and more bug fixes:

• ThemeListener is now able to properly switch between the light and dark theme.
• Fixed a bug where we were trying to navigate to wwwroot/index.html from the wrong root directory. I think in the future we should consider using an embedded resource instead, if possible.
• Tiny refactoring in DevToys MacOS's BlazorWebView.

Quality check

Before creating this PR:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• Did you build the app and test your changes?
• Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• Did you verify that the change work in Release build configuration
• Did you verify that all unit tests pass
• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS (DevToys 2.0)
  • Linux (DevToys 2.0)